The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
As is known in itself, an aircraft propulsion assembly traditionally comprises a turbojet engine housed inside a nacelle.
The nacelle generally has a tubular structure comprising an air intake upstream from the turbojet engine, a middle section intended to surround a fan of the turbojet engine and its casing, and a downstream section intended to surround the combustion chamber of the turbojet engine and, if applicable, housing thrust reverser means. It may end with a jet nozzle whereof the outlet is situated downstream from the turbojet engine.
Modern nacelles are intended to house a dual flow turbojet engine capable of using the rotating blades of the fan to generate a hot air flow (also called primary flow) coming from the combustion chamber of the turbojet engine, and a cold air flow (secondary flow) that circulates outside the turbojet engine through an annular passage, also called a tunnel, formed between the fairing of the turbojet engine and an inner wall of the nacelle. The two flows of air are ejected from the turbojet engine through the rear of the nacelle.
The role of a thrust reverser is to improve the braking capacity of an airplane during landing by reorienting at least part of the thrust generated by the turbojet engine forward. During that phase, the reverser obstructs the cold flow tunnel and orients said flow toward the front of the nacelle, thereby generating a counterthrust added to the braking of the wheels of the airplane.
The means used to perform this reorientation of the cold flow vary depending on the type of reverser. However, in all cases, the structure of a reverser comprises moving cowls that can be moved between the deployed position in which they open a passage in the nacelle intended for the deflected flow on the one hand, and a retracted position in which they close that passage on the other hand. These cowls may perform a deflecting function (pivoting door reverser) or simply serve to activate other deflecting means.
In the case of a grid reverser, also called a cascade reverser, the flow of air is reoriented using cascade vanes, the cowl performing a simple sliding function aiming to expose or cover said vanes. Additional blocking doors, also called flaps, activated by the sliding of the cowling, generally allow the tunnel to be closed downstream from the vanes so as to provide the reorientation of the cold flow.
In order to support the moving reverser cowls and connect the downstream section to the rest of the nacelle, and in particular the middle section by means of the fan casing, the downstream section comprises stationary elements and in particular longitudinal beams connected upstream to a substantially annular assembly called the front frame, formed by one or more parts between the longitudinal beams, and intended to be fastened to the periphery of the downstream edge of the casing of the engine fan.
This front frame is connected to the fan casing by fastening means generally of the blade/groove type comprising a substantially annular flange, made in one or more parts, secured to the front frame and cooperating with a J- or V-shaped slot. The fastening assembly is commonly referred to as a J-ring.
More generally, the parts of the rear section that are kept stationary during flight, namely the inner structure as well as the outer structure of the downstream section, are generally connected to the middle section or the fan casing using such a blade/groove flanging system.
The technological background is illustrated by document GB 2,384,827. Such a device works for C-duct or D-duct nacelles, i.e., whereof the downstream structure is made in the form of two half-parts that are substantially semi-cylindrical, mounted so as to be able, in particular during maintenance operations, to be opened “butterfly style” by pivoting around a substantially longitudinal hinge line situated near a connecting pylon to an aircraft.
In such a configuration, a blade/groove type connection is of course extremely advantageous, since while providing longitudinal strength, this type of connection also allows relatively easy removal of the blade or the groove in a radial direction during opening of the half-parts.
Recently, nacelles having other configurations have been developed, and in particular O-duct nacelles. Such nacelles do not have two substantially semi-cylindrical half-parts, but a single substantially peripheral cowl with a quasi-annular shape.
In such a configuration, the opening of the downstream section is no longer done by pivoting around a hinge line, but by sliding along guide rails positioned on either side of the attachment pylon.
Such a nacelle is in particular described in documents FR 2,907,098, FR 2,911,372, and FR 2,952,908.
A connecting device of the blade/groove type is then no longer suitable for this type of O-duct nacelle, in which the rear part can slide during maintenance operations (O-duct nacelle) toward the rear of the nacelle in a substantially longitudinal direction thereof.
In fact, in such a nacelle configuration, one or more areas of the downstream section should be provided opening laterally so as to be able to move the flange away from the grooves and free the front frame from the casing.
One solution to this type of problem has been described in document FR 2,970,513.